Supreme Instruments 385 Automatic Tester
Overview
The Supreme Instruments Model 385 Automatic (1935, $77.95, Supreme Instruments Corp., Greenwood, Mississippi) is a Depression-era combination instrument — an emission ("Quality Test") tube tester + set analyzer + VOM + capacitor tester — in a wood case with two 5-inch fan-shaped meters. Emission testers measure only whether the cathode still emits enough electrons under a specified load — they do not measure Gm, so they don't catch a tube that has lost transconductance while retaining emission (the exact debate the 385's own manual stages against building a Gm tester). Paired on Jeff's bench with the Heathkit TT-1 (a true Gm tester) — the emission-vs-Gm contrast.
Context
Supreme Instruments (Greenwood MS, 1926 → acquired by Hickok 1956) was an active mid-tier US test-equipment maker known for analyzers and tube testers; the 385 is one of their most ambitious units. Pair it with the Heathkit TT-1 (Gm tester) and the eTracer / uTracer6 (curve tracers) for the full triage spectrum. Common service issues on a unit this old: the original line cord + 1 A primary fuse; reform/replace the electrolytics; the copper-oxide rectifier ages (throws off AC-volts cal — it is NOT selenium, so don't swap in a silicon/selenium stack without recalibrating the whole AC network trimmed to its curve); the AC-multiplier caps C1–C6 and the neon blocking cap C1 are calibration elements (match value/tolerance, not just "bypass"); clean the many rotary selectors + circuit-breaking twin jacks; the two fan meters often need cleaning + rezero; source the Tube List card (on the Supreme archive) — the tester can't grade tubes without it.
